This invention relates to polysilanes of the average formula EQU [RSi][R.sub.2 Si][R.sub.d '(CH.sub.2 .dbd.CH)Si]
where there is present 0 to 60 mole percent of [R.sub.2 Si] units, 30 to 99.5 mole percent of [RSi] units, and 0.5 to 15 mole percent of [R.sub.d '(CH.sub.2 .dbd.CH)Si] units. This invention also relates to the methods of preparing such polysilanes as well as silicon carbide ceramics prepared from such polysilanes. The vinyl-containing polysilanes of this invention may be rendered infusible by exposure to UV irradiation in an inert atmosphere prior to pyrolysis to form ceramic material. Such cure mechanisms can result in ceramic materials containing only limited amounts of oxygen.
Baney et al. in U.S. Pat. No. 4,310,651 (issued Jan. 12, 1982) disclosed a polysilane of general formula EQU [CH.sub.3 Si][(CH.sub.3).sub.2 Si]
where there was present 0 to 60 mole percent [(CH.sub.3).sub.2 Si] units and 40 to 100 mole percent [CH.sub.3 Si] units and where the remaining bonds on silicon were attached to other silicon atoms and chlorine atoms or bromine atoms. The polysilane was converted to a beta-silicon carbide containing ceramic at elevated temperatures (about 1400.degree.0 C.). The polysilanes of U.S. Pat. No. 4,310,651 generally are difficult to handle due to their high reactivity in air.
Baney et al. in U.S. Pat. No. 4,298,559 (issued Nov. 3, 1981) prepared polysilanes of general formula EQU [CH.sub.3 Si][(CH.sub.3).sub.2 Si]
where there was present 0 to 60 mole percent [(CH.sub.3).sub.2 Si] units and 40 to 100 mole percent [CH.sub.3 Si] units and where the remaining bonds on silicon were attached to other silicon atoms and additional alkyl radicals of 1 to 4 carbon atoms or phenyl radicals. Upon heating these polysilanes were converted into silicon carbide containing ceramics in high yields.
Baney et al. in U.S. Reissue Pat. No. Re. 31,447 (reissued Nov. 22, 1983) disclosed polysilanes of the general formula EQU [CH.sub.3 Si][(CH.sub.3).sub.2 Si]
where there was present 0 to 60 mole percent [(CH.sub.3).sub.2 Si] units and 40 to 100 mole percent [CH.sub.3 Si] units and where the remaining bonds on silicon were attached to other silicon atoms and alkoxy radicals containing 1 to 4 carbon atoms or phenoxy radicals. Silicon carbide ceramics were obtained by firing these polysilanes to elevated temperatures.
Baney et al. in U.S. Pat. No. 4,314,956 (issued Feb. 9, 1982) disclosed polysilanes of the general formula EQU [CH.sub.3 Si][(CH.sub.3).sub.2 Si]
where there was present 0 to 60 mole percent [(CH.sub.3).sub.2 Si] units and 40 to 100 mole percent [CH.sub.3 Si] units and where the remaining bonds on silicon were attached to silicon and amine radicals of the general formula --NHR.sup.vi where R.sup.vi is a hydrogen atom, an alkyl radical of 1 to 4 carbon atoms or a phenyl radical. A silicon carbide ceramic was obtained by firing this polysilane to an elevated temperature under an inert atmosphere or under an ammonia atmosphere.
The just disclosed U.S. Pat. Nos. 4,310,651; 4,298,599; Re 31,447; and 4,314,956 are hereby incorporated by reference. These polysilanes are further discussed in Baney et al. Organometallics, 2, 859 (1983).
West in U.S. Pat. No. 4,260,780 (issued Apr. 7, 1981) prepared a polysilane of general formula EQU [(CH.sub.3).sub.2 Si][CH.sub.3 (C.sub.6 H.sub.5)Si]
by the sodium metal reduction of dimethyldichlorosilane and methylphenylsilane. The resulting methylphenylpolysilanes had very high softening points (&gt;280.degree. C.).
West et al. in Polym. Prepr., 25, 4 (1984) disclosed the preparation of a polysilane of general formula EQU [CH.sub.3 (CH.sub.2 .dbd.CHCH.sub.2)Si][CH.sub.3 (C.sub.6 H.sub.5)Si]
by the sodium metal reduction of allylmethyldichlorosilane and methylphenyldichlorosilane. These polysilanes were rapidly gelled by irradiation with ultraviolet light.
It has now been determined that polysilanes of the average formula EQU [RSi][R.sub.2 Si][R.sub.d '(CH.sub.2 .dbd.CH)Si]
may be prepared in good yield. These polysilanes may be pyrolyzed at elevated temperatures in an inert atmosphere to produce silicon carbide-containing ceramics. The polysilanes may be cured, and thus rendered infusible, prior to pyrolysis by exposure to ultraviolet light.